This invention generally relates to battery cathodes.
Batteries are commonly used electrical energy sources. A battery contains a negative electrode, typically called an anode, and a positive electrode, typically called a cathode. The cathode may include a positive active material (e.g., a transition metal oxide such as MnO2) that can be reduced, a conductive aid (e.g., graphite), and a binder (e.g., polyethylene (PE)). The anode can be a gel including an active material (e.g., zinc particles) that can be oxidized. The anode active material is capable of reducing the cathode active material. In order to prevent direct reaction of the anode material and the cathode material, the anode and the cathode are electrically isolated from each other by a separator.
When the battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
Alkaline batteries include cylindrical batteries, for example, the conventional AA, AAA, AAAA, C, and D batteries, commonly sold in stores. These conventional alkaline batteries include a cylindrical container (called a can) containing a central, cylindrical gel anode surrounded by a hollow cylindrical transition metal oxide cathode.
A cylindrical cathode can be made by a number of ways. One method is to place a number of ring-shaped discs in the can to form a tall, loose fitting hollow cylinder. The discs are reformed in the can to provide good contact to the can wall by placing a core rod in the cavity of the cylinder and re-compacting the discs by applying pressure to the top of the discs. The discs can also be made oversized, i.e., the outer diameter of the discs is bigger than the inner diameter of the can, and force fit into the can by inserting them through a tapered funnel. Another method of making the cathode includes placing cathode powder or granules in the can and forming the cathode by driving a central core rod into the powder while restraining the powder on the top surface of the cathode with a punch. Cathodes made by these methods can have shiny, glazed surfaces with closed pores.